1. Field of the Invention
The invention relates to extraction to separate asphaltenic and maltenic material from residua and heavy oils. More particularly, it concerns the use of two or more solvents of differing polarity to effect such extraction.
2. Discussion of the Prior Art
Solvent deasphalting is a well-known operation in refineries. The primary objective of deasphalting is to separate a petroleum stream into a relatively high quality fraction ("deasphalted oil" or "maltenes") and a lower quality fraction ("asphalt" or "asphaltenes"). The asphaltenes are generally higher in aromaticity, Conradson Carbon Residue (CCR), molecular weight, and heteroatom (S, N, Ni, V, Fe, etc.) content. Conversely, the maltenes are generally lower in these. Solvent deasphalting may also be thought of as a simple form of compositional delineation. Many methods have been used in the past, and many are currently available for separating hydrocarbons into their more distinct compositional groups. One available method is gradient elution chromatography. Another method is deasphalting with liquid propane.